1. Field of the Invention
The present invention relates to improvements in apparatus for recording or analyzing jaw movements.
2. Description of the Prior Art
In analyzing and treating jaw disorders and in making dental prosthesis, it is desirable to simulate the individual patient's jaw movements. To do this on a dental articulator, it is first necessary to analyze the jaw movements and it is desirable that the apparatus be available to quickly and accurately perform such functions.
One system for analyzing jaw movements is set forth in U.S. Pat. No. RE 31,615 to Robert L. Lee, wherein an upper frame or face bow is mounted on a patient's nose and ears with side arms supporting rigid recording plates overlying the patient's temporomandibular joints. A grid of intersecting lines on graph paper is provided on the recording plates. A lower or mandibular frame is mounted by means of a dental clutch to the patient's lower jaw so as to move with the jaw. Side arms of the lower frame carry writing elements for tracing on the graphs jaw movements.
In use of such apparatus, it is usually initially necessary to locate the hinge axis about which the lower jaw rotates when it is in its rearward most position and moved in mouth closing and opening directions. The writing element will trace an arc on the graph paper unless the element is on the hinge axis. If the element remains stationary, making a single point on the graph paper, the hinge axis of the patient's jaw has been located. Normally as initially mounted, the writing element or stylus carrying the element is not on the hinge axis and hence it is necessary to make suitable adjustments to move the stylus so that it is on the axis. Typically, the lower head frame has two parallel side arms mounted by suitable clamps to a forward transverse rod, which is perpendicular to the side arms. In the aforementioned patent, the front-to-rear location of the stylus is varied by rotating an adjustment screw which changes the length of the side arm in relation to its attachment point on the transverse rod. The vertical location of the stylus is changed by way of a second adjustment screw which moves the side arm in an arc about the transverse rod. While this approach is capable of making precise incremental adjustments in the location of the stylus, it takes considerable time and skill to move the side arm so that the stylus is aligned with the hinge axis. After an adjustment is made, it is necessary to hinge the jaw to see whether an arc is being made by the stylus or whether it is on the axis. Typically, an adjustment will be made which moves to the other side of the axis, and it is necessary to make further smaller adjustments until the proper location is reached. Frequently, new operators will make mistakes in this process such as rotating an adjustment screw in the wrong direction. U.S. Pat. No. 3,035,348-Page also shows a system employing adjustment screws for locating the hinge axis wherein considerable time and skill is required.
Another known, simpler system employs a clamp connecting the side arms of a lower frame to the forward transverse rod wherein the side arm is slidable front-to-rear in the clamp and is rotatable with the clamp about the transverse rod. A clamping screw holds the side arm in a selected front to rear and rotational position. While such a system is simple in construction, it does not work very well because loosening the clamping screw permits the arm to fall or move in both of its adjustment directions, and it is difficult to make both the angular and the front-to-rear adjustments at one time and then tighten the clamp screw to hold the arm in the selected position. If the selected position is incorrect, it is necessary to unloosen the clamping screw, and the prior position that might have been fairly close to being correct is often lost such that the process must be repeated several times before proper adjustment is made.
It is, therefore, desireable to have a mounting arrangement which will permit the practitioner to readily adjust the arcuate position and the front-to-rear position of a side arm in a minimum amount of time. Further, it is desirable that the apparatus be capable of independent adjustment of the position of each side arm.